Tube systems for ventilation (also known as respiration) with two separate tube volumes extending in parallel have been sufficiently well known from the state of the art. They are used preferably in the field of medicine, especially for the purposes of ventilating patients, and they have an inspiratory line and an expiratory line connected to it, which facilitates the use.
For example, it is known from the state of the art that two ventilation lines that are separated from one another can be provided by a tube with an axially extending, membrane-like partition being provided, so that two volumes that are separated from one another are generated thereby. However, the length of the tube system is defined as a fixed value in this variant (for example, Limb-O variant of Vital Signs).
The tube system may also be designed as a coaxial tube system with an outer tube and an inner tube with a smaller diameter, and both tubes are usually designed as corrugated tubes in order to ensure the necessary flexibility. Furthermore, coaxial tube systems are known as well, whose length is variable. This property of a variable tube length is achieved by the outer tube and the inner tube being designed each as a folded tube, in which the folds spread out during longitudinal extension. Coaxial tube systems with the possibility of varying the length have the advantage over tube systems with fixed lengths that tube systems with different lengths are not needed for different applications, and, for example, the storage expenses of a medical institution is not increased due to the need to stock the tube systems in a plurality of lengths. Furthermore, situations in which a flexible length adaptation is desirable, for example, when changing the position of patients, may occur during the use of the tube systems.
However, the tubes are connected to one another at their respective ends only in the coaxial tube systems with outer tube and inner tube and are in an undefined position in relation to one another between the ends. The coaxial tube systems with fixed or variable length known from the state of the art have the following drawback due to this design. First, the often sharp-edged folds of the inner tube and of the outer tube, which are needed for the flexibility and possibly for extensibility, generate a turbulent flow of the gas in areas in which the gap between the inner tube and the outer tube does not reach a critical value, which will then lead, on the whole, to an increased flow resistance for the gas.